This invention relates to aluminum compositions useful in water treatment and to methods for the manufacture and use thereof.
Aluminum sulfate (alum), aluminum chloride, and basic aluminum species derived therefrom are known to be useful in the treatment of both potable and waste water. For example, the use of alum as a water treatment chemical is described generally in U.S. Pat. No. 3,959,133. Basic aluminum sulfate (BAS), basic aluminum chloride (BAC) and basic aluminum chloride sulfate (BACS) are discussed in U.S. Pat. Nos. 1,137,005, 3,440,008, 3,544,476, 3,929,666, 4,051,028, 4,069,299, 4,238,347, 4,284,611, British Pat. No. 442,144 and European Patent Appln. Nos. 0 005 419 and 0 017 634.
One known method for making basic aluminum compounds from alum involves precipitation of aluminum hydroxide from a dilute alum solution (approx. 1.2% Al.sub.2 O.sub.3) by addition of a base. The aluminum hydroxide precipitate is then separated from the remaining solution and is redissolved in a solution of either aluminum sulfate to form BAS or aluminum chloride to form BACS. In this method, however, the precipitation step can be lengthy, and the aluminum hydroxide recovered is difficult to filter and still contains a substantial amount of water, thus reducing the concentration of the final product achievable.